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Abstract:

Disclosed herein is a method for manufacturing a printed circuit board,
the method including: preparing a base substrate having a connection pad;
forming a surface treatment layer on the connection pad;
refrigeration-treating the base substrate having the connection pad on
which the surface treatment layer is formed; and printing a solder paste
on the connection pad of the refrigeration-treated base substrate.

Claims:

1. A method for manufacturing a printed circuit board, the method
comprising: preparing a base substrate having a connection pad; forming a
surface treatment layer on the connection pad; refrigeration-treating the
base substrate having the connection pad on which the surface treatment
layer is formed; and printing a solder paste on the connection pad of the
refrigeration-treated base substrate.

2. The method as set forth in claim 1, wherein the connection pad is made
of copper (Cu).

3. The method as set forth in claim 1, wherein the forming of the surface
treatment layer is performed by an electroless tin plating process.

4. The method as set forth in claim 1, wherein the refrigeration-treating
of the base substrate is performed for 1 to 2 hours.

5. The method as set forth in claim 1, wherein the refrigeration-treating
of the base substrate is performed at a temperature of 0.degree. C. to
5.degree. C.

6. The method as set forth in claim 1, wherein the solder paste is at
least one of a Sn--Pb based solder paste, a Sn--Ag solder paste, a Sn--Cu
solder paste, and a Sn--Ag--Cu solder paste.

7. The method as set forth in claim 1, further comprising, after the
printing of the solder paste, forming a solder bump by performing a
reflow process on the solder paste; and removing a flux remaining on a
surface of the solder bump.

8. The method as set forth in claim 1, wherein the preparing of the base
substrate includes: preparing a substrate on which an outermost layer of
circuit including the connection pad is formed; forming a solder resist
layer on the substrate; and forming an opening for exposing the
connection pad in the solder resist layer.

Description:

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of Korean Patent Application
No. 10-2011-0068004, filed on Jul. 8, 2011, entitled "Method for
Manufacturing Printed Circuit Board", which is hereby incorporated by
reference in its entirety into this application.

BACKGROUND OF THE INVENTION

[0002] 1. Technical Field

[0003] The present invention relates to a method for manufacturing a
printed circuit board.

[0004] 2. Description of the Related Art

[0005] A printed circuit board generally includes a connection pad exposed
to the outside so that components such as a semiconductor, or the like,
may be mounted thereon.

[0006] The connection pad is generally made of a copper (Cu) material.
However, since copper exposed to the outside may be oxidized and corroded
with the passage of time, a surface treatment layer is formed on the
exposed connection pad in order to prevent a damage of the exposed
connection pad.

[0007] Various methods for forming a surface treatment layer have been
currently used. Among them, there is an immersion tin (IT) plating
method, which is an electroless plating method. The immersion tin plating
method, which is an electroless tin plating method using an
oxidation/reduction potential between tin (Sn) and copper (Cu), has also
been widely used in a flexible circuit board (FCB) field.

[0008] The above-mentioned electroless tin plating method is excellent in
view of a cost as compared to a gold plating method. However, in the case
of the electroless tin plating method, a solder bump is separated from
the connection pad during a process of forming the solder bump, which is
a post-process.

[0009] That is, in the case in which the tin (Sn) is plated on the
connection pad made of the copper (Cu) through the electroless tin
plating, intermetallic compounds (hereinafter, referred to as `IMCs`)
called Cu3Sn are produced in a copper/tin interface due to a
difference in solid solubility of the tin (Sn) within the copper (Cu)
immediately after the plating. The IMCs produced as described above are
grown together with Cu6Sn5 during the progress of a process,
such that there are IMSs Cu3Sn and Cu6Sn5 having an
average thickness of about 0.68 μm in the copper (Cu)/tin (Sn)
interface as shown in FIG. 1.

[0010] As described above, as the IMCs are grown, a thickness of pure tin
(Sn) becomes relatively thinner than that of pure tin (Sn) immediately
after the plating as shown in FIG. 1, such that wettability between a
solder paste and the tin (Sn) interface is deteriorated. Therefore,
spreadability of a flux is deteriorated and interdiffusion between the
copper (cu) and the solder paste is hindered, such that the solder bump
is separated from the connection pad due to an insufficient reaction
between the connection pad and the solder paste after a reflow process is
performed.

SUMMARY OF THE INVENTION

[0011] The present invention has been made in an effort to provide a
method for manufacturing a printed circuit board capable of suppressing
growth of intermetallic compounds in an interface between a connection
pad made of copper (Cu) and a surface treatment layer made of tin (Sn).

[0012] Further, the present invention has been made in an effort to
provide a method for manufacturing a printed circuit board capable of
preventing separation of a solder bump formed on a connection pad.

[0013] According to a preferred embodiment of the present invention, there
is provided a method for manufacturing a printed circuit board, the
method including: preparing a base substrate having a connection pad;
forming a surface treatment layer on the connection pad;
refrigeration-treating the base substrate having the connection pad on
which the surface treatment layer is formed; and printing a solder paste
on the connection pad of the refrigeration-treated base substrate.

[0014] The connection pad may be made of copper (Cu).

[0015] The forming of the surface treatment layer may be performed by an
electroless tin plating process.

[0016] The refrigeration-treating of the base substrate may be performed
for 1 to 2 hours and be performed at a temperature of 0° C. to
5° C.

[0017] The solder paste may be at least one of a Sn--Pb based solder
paste, a Sn--Ag solder paste, a Sn--Cu solder paste, and a Sn--Ag--Cu
solder paste.

[0018] The method may further include, after the printing of the solder
paste, forming a solder bump by performing a reflow process on the solder
paste; and removing a flux remaining on a surface of the solder bump.

[0019] The preparing of the base substrate may include: preparing a
substrate on which an outermost layer of circuit including the connection
pad is formed; forming a solder resist layer on the substrate; and
forming an opening part exposing the connection pad in the solder resist
layer.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] FIG. 1 is a view showing a state in which intermetallic compounds
(IMCs) are grown in an interface between a connection pad (Cu) and a
surface treatment layer (Sn) of a printed circuit board formed according
to the prior art;

[0021]FIG. 2 is a flow chart showing a method for manufacturing a printed
circuit board according to a preferred embodiment of the present
invention;

[0022]FIG. 3 is a view showing a state of an interface between a
connection pad (Cu) and a surface treatment layer (Sn) of a printed
circuit board formed by a method for manufacturing a printed circuit
board according to a preferred embodiment of the present invention;

[0023] FIG. 4 is a graph showing growth thicknesses of IMCs for each
process condition (temperature); and

[0024]FIG. 5 is a graph showing a degree of scattering of thicknesses of
IMCs for each process condition (temperature).

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] Various features and advantages of the present invention will be
more obvious from the following description with reference to the
accompanying drawings.

[0026] The terms and words used in the present specification and claims
should not be interpreted as being limited to typical meanings or
dictionary definitions, but should be interpreted as having meanings and
concepts relevant to the technical scope of the present invention based
on the rule according to which an inventor can appropriately define the
concept of the term to describe most appropriately the best method he or
she knows for carrying out the invention.

[0027] The above and other objects, features and advantages of the present
invention will be more clearly understood from preferred embodiments and
the following detailed description taken in conjunction with the
accompanying drawings. In the specification, in adding reference numerals
to components throughout the drawings, it is to be noted that like
reference numerals designate like components even though components are
shown in different drawings. Further, when it is determined that the
detailed description of the known art related to the present invention
may obscure the gist of the present invention, the detailed description
thereof will be omitted. In the description, the terms "first", "second",
and so on are used to distinguish one element from another element, and
the elements are not defined by the above terms.

[0028] Hereinafter, preferred embodiments of the present invention will be
described in detail with reference to the accompanying drawings.

[0029]FIG. 2 is a flow chart showing a method for manufacturing a printed
circuit board according to a preferred embodiment of the present
invention.

[0030] A base substrate having a connection pad is first prepared (S201).

[0031] According to the present embodiment, the preparing of the base
substrate may include preparing a substrate on which an outermost layer
of circuit including the connection pad is formed, forming a solder
resist layer on the substrate, and forming an opening part exposing the
connection pad in the solder resist layer.

[0032] Here, the opening part may be formed by a photolithography method
or a laser method including exposure and development.

[0033] The base substrate, which is a circuit substrate on which at least
one layer of circuit including the connection pad is formed on an
insulating layer thereof, may be a printed circuit board.

[0034] As the insulating layer, a resin insulating layer may be used. As
materials of the resin insulating layer, a thermo-setting resin such as
an epoxy resin, a thermo-plastic resin such as a polyimide resin, a resin
having a reinforcement material such as a glass fiber or an inorganic
filler impregnated in them, for example, a prepreg may be used. In
addition, a thermo-setting resin, a photo-setting resin, and the like,
may be used. However, the materials of the resin insulating layer are not
specifically limited thereto.

[0035] In addition, the circuit including the connection pads may be made
of any material used as a conductive metal for a circuit in a circuit
substrate field, and is typically made of copper in the case of a printed
circuit board.

[0036] The solder resist layer serves as a protective layer protecting the
outermost layer of circuit of the printed circuit board, is formed for
electrical insulation, and includes the opening part formed in order to
expose the outermost layer of connection pad. A solder resist configuring
the solder resist layer may be, for example, solder resist ink, a solder
resist film, an encapsulant, or the like, as known in the art, but is not
specifically limited thereto.

[0037] Then, a surface treatment layer is formed on the connection pad
(S203).

[0038] A process for forming the surface treatment layer may be generally
divided into an electro gold plating process, an immersion gold plating
process, an organic solderability preservative (OSP) or immersion tin
plating process, an immersion silver plating process, an electroless
nickel and immersion gold (ENIG) process, a direct immersion gold (DIG)
plating process, a hot air solder leveling (HASL) process, or the like.
According to the present embodiment, the surface treatment layer is
formed by using the immersion tin plating process.

[0039] Next, the base substrate having the surface treatment layer, for
example, a tin plating layer, formed on the connection pad thereof is
refrigeration-treated (S205).

[0040] Here, the refrigeration-treating may be performed by storing the
base substrate in an apparatus in which the base substrate may be stored
in a low temperature state for a predetermined time.

[0041] According to the present embodiment, the base substrate is
refrigeration-treated at a temperature of 0 to 5° C. for about 1
to 2 hours.

[0042] During a real process for manufacturing a printed circuit board, a
work-in-process congestion phenomenon in which a process for forming a
solder bump may not be performed immediately after the surface treatment
layer is formed on the connection pad of the base substrate is frequently
generated.

[0043] As time passes in a state in which the solder bump is not formed
after the formation of the surface treatment layer due to the
work-in-process congestion, Cu3Sn, which is an intermetallic
compound (IMC) between copper (Cu) and tin (Sn) produced in an interface
between the connection pad and the surface treatment layer is grown
Cu6Sn5. However, when the base substrate having the surface
treatment layer formed thereon is refrigeration-treated under the
above-mentioned temperature and time condition, growth of the IMCs in the
interface between the connection pad and the surface treatment layer may
be suppressed until a process for forming a solder bump, which is a
subsequent process, is performed.

[0044] A state of the base substrate after the refrigeration-treating
process is performed on the base substrate under the above-mentioned
condition, for example, at a temperature of 0 to 5° C. for about 1
to 2 hours and a predetermined period (a week in the present embodiment)
then passes is shown in FIG. 3. Referring to FIG. 3, it may be
appreciated that the IMCs have scarecely been grown in the interface
between the connection pad made of Cu and the surface treatment layer,
which is the tin (Sn) plating layer.

[0045] Thereafter, a solder paste is printed on the connection pad of the
refrigeration-treated base substrate (S207).

[0046] Here, as a method for printing the solder paste, a method of
disposing a mask including an aperture part formed at a position
corresponding to the connection pad on the base substrate and filling the
solder paste in the aperture part using a squeegee may be generally used.
However, the method for printing the solder paste is not specifically
limited thereto.

[0047] Here, the solder paste may be configured of 50 wt % of solder
particle components and 50 wt % of flux components combining the solder
particle components to each other but is not specifically limited
thereto.

[0048] In addition, the solder paste may be at least one of a Sn--Pb based
solder paste, a Sn--Ag solder paste, a Sn--Cu solder paste, and a
Sn--Ag--Cu solder paste but is not specifically limited thereto.

[0049] Then, a solder bump is formed by performing a reflow process on the
solder resist (S209).

[0050] The reflow process, which is a process for melting the solder paste
to thereby attach the solder past to the connection pad, is performed
after the mask that has been disposed on the base substrate in order to
print the solder paste is removed. The reflow process may be generally
performed at a maximum temperature of 200 to 300° C. but is not
specifically limited thereto. For example, a reflow temperature may be
changed according to components contained in the solder paste.

[0051] Most of the flux components mixed with the solder paste are
volatilized at the time of the reflow. However, since some of the flux
components may remain in the solder bump without being volatilized, a
deflux process of cleaning and removing the flux components remaining in
the solder bump and the connection pad may be additionally performed.

[0052] The following Table 1 shows experimental data obtained by comparing
solder bump separation ratios of each of the base substrates each having
the surface treatment layer formed on the connection pad made of the
copper (Cu) through the electroless tin plating process and being
subjected to refrigeration-treatment at temperatures of 0° C.,
3° C., and 5° C. for 1 hour with a solder bump separation
ratio of a base substrate being not subjected to the
refrigeration-treatment.

[0053] After a predetermined period (a week in the present embodiment)
passes, each of the solder bumps was formed on each of the connection
pads of the base substrates each being subjected to the
refrigeration-treatment and being not subjected to the
refrigeration-treatment.

[0054] As shown in Table 1, it may be appreciated that the separation
ratio in which the solder bump formed on the connection pad of the base
substrate being subjected to the refrigeration-treatment at a temperature
of 0 to 5° C. for about 1 hour is separated from the connection
pad is significantly lower than that of the solder bump formed on the
connection pad of the base substrate being not subjected to the
refrigeration-treatment

[0055] In addition, the correlation between thicknesses of IMCs formed in
the interface between the connection pad and the surface treatment layer
of each of the base substrates being subjected to the
refrigeration-treatment at temperatures of 0° C., 3° C.,
and 5° C. for 1 hour and the base substrate being not subjected to
the refrigeration-treatment, and whether or not the
refrigeration-treatment is performed and the refrigeration-treatment
temperature is shown in a graph of FIG. 4.

[0056] In FIG. 4, an X axis indicates cases in which the
refrigeration-treatment is performed at temperatures of 0° C.,
3° C., and 5° C., respectively, and a case in which the
refrigeration-treatment is not performed, and a Y axis indicates a
thickness of the IMC produced in the interface between the connection pad
(Cu) and the surface treatment layer (Sn).

[0057] Referring to FIG. 4, measurement values of thicknesses of IMCs
produced in interfaces between connection pads and surface treatment
layers of a plurality of base substrates being subjected to
refrigeration-treatment at a temperature of 0° C. are represented
by a plurality of points. Likewise, measurement values of thicknesses of
IMCs produced in a plurality of base substrates being subjected to
refrigeration-treatment at temperatures of 3° C. and 5° C.
and IMCs produced in a plurality of base substrates being not subjected
to the refrigeration-treatment are represented by a plurality of points.

[0058] Here, a central tetragonal box indicates a range in which the
measurement values are distributed, and marks `-` over and under the
central tetragonal box indicate the maximum and minimum values of the
measured thicknesses.

[0059] A standard deviation of remaining values except for the maximum and
minimum values of the measured thicknesses was calculated, and a degree
of scattering of thicknesses of IMCs produced for each process condition
(temperature) was shown in a graph of FIG. 5.

[0060] Referring to FIG. 5, a degree of scattering of thicknesses of the
IMCs produced in the plurality of base substrates being subjected to the
refrigeration-treatment at a temperature of 0° C. was
approximately 0.036, a degree of scattering of thicknesses of the IMCs
produced in the plurality of base substrates being subjected to the
refrigeration-treatment at a temperature of 3° C. was
approximately 0.041, a degree of scattering of thicknesses of the IMCs
produced in the plurality of base substrates being subjected to the
refrigeration-treatment at a temperature of 5° C. was
approximately 0.058, and a degree of scattering of thicknesses of the
IMCs produced in the plurality of base substrates being not subjected to
the refrigeration-treatment was approximately 0.101.

[0061] Here, it may be appreciated that the thickness of the IMC produced
in the base substrate being subjected to the refrigeration-treatment is
relatively more uniform than that of the IMC produced in the base
substrate being not subjected to the refrigeration-treatment.

[0062] As such, the surface treatment layer is formed on the connection
pad of the base substrate and the base substrate is then
refrigeration-treated at a predetermined temperature for a predetermined
time, thereby making it possible to suppress the growth of the IMC in the
interface between the connection pad and the surface treatment layer.

[0063] As described above, the growth of the IMC is suppressed to prevent
the thickness of pure tin (Sn), which is the surface treatment layer,
from being thinned, such that the spreadabilities of the solder paste and
the flux on the surface treatment layer are improved and the
interdiffusion between the connection pad (Cu) and the solder paste is
smoothly performed, thereby making it possible to prevent the solder bump
from being separated from the connection pad after the reflow.

[0064] As set forth above, according to the preferred embodiment of the
present invention, the surface treatment layer is formed on the
connection pad made of the copper (Cu) through the electroless tin
plating process and is then subjected to the refrigeration-treatment for
a predetermined time, thereby making it possible to suppress the growth
of the IMC in the interface between the connection pad and the surface
treatment layer.

[0065] In addition, according to the preferred embodiment of the present
invention, the growth of the IMC in the interface between the connection
pad and the surface treatment layer is suppressed, thereby making it
possible to prevent the solder bump formed on the connection pad from
being separated from the connection pad.

[0066] Further, according to the preferred embodiment of the present
invention, the separation of the solder bump from the connection pad is
prevented as described above, thereby making it possible to reduce a
product defect and a manufacturing cost.

[0067] Although the preferred embodiments of the present invention have
been disclosed for illustrative purposes, they are for specifically
explaining the present invention and thus a method for manufacturing a
printed circuit board according to the present invention is not limited
thereto, but those skilled in the art will appreciate that various
modifications, additions and substitutions are possible, without
departing from the scope and spirit of the invention as disclosed in the
accompanying claims.

[0068] Accordingly, such modifications, additions and substitutions should
also be understood to fall within the scope of the present invention.

Patent applications by Su Jin Lee, Busan KR

Patent applications by Young Kwan Lee, Busan KR

Patent applications by Samsung Electro-Mechanics Co., Ltd.

Patent applications in class With pretreating other than heating or cooling of work part of filler prior to bonding and any application of filler

Patent applications in all subclasses With pretreating other than heating or cooling of work part of filler prior to bonding and any application of filler